Combined lighting, projection, and image capture without video feedback

ABSTRACT

A “Concurrent Projector-Camera” uses an image projection device in combination with one or more cameras to enable various techniques that provide visually flicker-free projection of images or video, while real-time image or video capture is occurring in that same space. The Concurrent Projector-Camera provides this projection in a manner that eliminates video feedback into the real-time image or video capture. More specifically, the Concurrent Projector-Camera dynamically synchronizes a combination of projector lighting (or light-control points) on-state temporal compression in combination with on-state temporal shifting during each image frame projection to open a “capture time slot” for image capture during which no image is being projected. This capture time slot represents a tradeoff between image capture time and decreased brightness of the projected image. Examples of image projection devices include LED-LCD based projection devices, DLP-based projection devices using LED or laser illumination in combination with micromirror arrays, etc.

BACKGROUND

1. Technical Field

A “Concurrent Projector-Camera” uses an image projection device incombination with one or more digital cameras and optional lighting toenable various techniques that provide visually flicker-free projectionconcurrently with real-time image or video capture in the same space ina manner that eliminates video feedback from the projection into thereal-time image or video capture.

2. Background Art

If two or more people are trying to share a common desktop where eachhas a camera and a projector, a video feedback loop will be createdcausing the video to become useless in a manner similar to audiofeedback which results in high pitch squealing. This problem has beenreferred to as “visual echo.”

More specifically, “visual echo” represents the appearance of theprojected contents viewed by a camera back into the projection overtime. This problem is analogous to audio or acoustic echo in telephonecommunications where the person speaking hears a delayed version of hisown voice that may become increasingly corrupted by ongoing echo overtime. As with acoustic echo cancellation, visual echo cancellation hasbeen performed using a variety of techniques, some of which requiresignificant computational resources.

For example, one conventional visual echo cancellation scheme forsharing a virtual workspace or virtual whiteboard between separatelocations uses a setup in which the captured video at each locationcontains local writings or user gestures (i.e., the “foreground”) alongwith projected contents representing the shared workspace. Therefore, ifthe captured video is simply broadcast to each separate location, therewill be a feedback loop that will distort the projected image. In fact,after only a few frames, some parts of the projected image will becomesaturated while some parts of the real (i.e., local) writing will appearto have a ghosting effect. This problem is addressed by using anoff-line calibration procedure that records a geometric and photometrictransfer between the projector and the camera in a look-up table. Then,during run-time, projected contents in the captured video are identifiedusing the calibration information and computationally suppressed,therefore achieving the goal of canceling visual echo.

Another conventional approach to visual echo cancellation synchronizes afast switching DLP projector and a camera, so that the camera takes animage only when the projector is off or showing a specific pattern. Thiseffectively interleaves the operation of the projector and camera in atime-sequential manner using default projector timings. The use of afast-switching DLP projector avoids visual flicking. While this approachavoids visual echoes by interleaving projection and image captureoperations, it requires careful analysis of the DLP projector colorwheel and mirror flip timing for synchronizing camera activation timingin a manner that ensures that images are only captured when the DLPprojector is either off or is projecting a known pattern. It has beensuggested that such systems are difficult to implement and to accuratelysynchronize. A related approach simply prevented one or more entireframes from being projected to provide a time during which images couldbe captured by a co-located camera.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. Further, while certain disadvantages of prior technologies maybe noted or discussed herein, the claimed subject matter is not intendedto be limited to implementations that may solve or address any or all ofthe disadvantages of those prior technologies.

In general, a “Concurrent Projector-Camera,” as described herein, usesan image projection device in combination with one or more digitalcameras to enable various techniques that provide visually flicker-freeprojection of recorded or real-time images or video, while real-timeimage or video capture is occurring in approximately that same space(which includes a sub-region of the projection area, the entireprojection area or extended region encompassing the projection area).Note that rather than repeatedly describing the range of areas in whichthe camera or cameras are capturing the scene or projection space, thefollowing discussion will generally simply refer to using the camera orcameras to capture the projection area. Further, the ConcurrentProjector-Camera provides these capabilities in a manner that eliminatesvideo feedback from the projection into the real-time image or videocapture. Note that this process differs from conventional techniquesthat attempt to interleave image capture and image projection withoutdynamically modifying projector timing. Examples of image projectiondevices that may be adapted for use by the Concurrent Projector-Camerainclude, but are not limited to, LED-LCD based projection devices,DLP-based projection devices using LED or laser illumination incombination with micromirror arrays or LCD shutters, etc.

More specifically, the Concurrent Projector-Camera dynamicallysynchronizes a combination of projector lighting on-state temporalcompression in combination with on-state temporal shifting to open anintra-frame “capture time slot” for image capture during which no imageis being projected. This capture time slot is created during the periodin which a single image frame is being projected (hence the use of theterm “intra-frame”), and represents a tradeoff between image capturetime and decreased brightness of the projected image frame.Significantly, these capabilities are achieved without cancelling oreliminating entire projection frames, as is the case with variousconventional techniques.

In other words, the Concurrent Projector-Camera dynamically controls animage projection device to create a capture time slot, during which noimage is being projected. Therefore, this capture time slot allowsimages to be captured of the projection area without being corrupted bythe projection. Further, the image capture enabled by the ConcurrentProjector-Camera can be achieved at a frame rate at least as high as theframe rate of the projector, thereby enabling a wide variety ofapplications involving real-time multi-site video communications.Advantageously, all of these real-time multi-site video communicationsapplications are achieved while completely eliminating any possibilityof “visual echo” from any projection into any captured image that isthen transmitted or broadcast to another location.

For example, in the case of LED-LCD based projectors, the ConcurrentProjector-Camera creates the capture time slot by dynamically reducingor compressing the amount of time during which each LED is in anon-state during each image frame, as well as shifting those compressedLED on-state times within the time period for each image frameprojection. This synchronized combination of LED on-state temporalcompression and LED on-state temporal shifting opens a window of time(i.e., the aforementioned “capture time slot”) during which an image canbe captured by a camera without being corrupted by the projection.

Advantageously, when using small projectors (e.g., pico-projectors) incombination with relatively small cameras, the ConcurrentProjector-Camera can be implemented within a small form factor about thesize and configuration of a small desktop lamp. In fact, such a formfactor can include optional additional lighting that allows theConcurrent Projector-Camera to function as a lamp when not being usedfor other purposes such as providing scene illumination for the camera.For example, desktop lamps come in many configurations that can eitherbe set onto a desktop surface to provide illumination of that surface,or can be clamped or attached to an edge of a desktop surface or othernearby object or wall. The Concurrent Projector-Camera can also beimplemented within other lighting-type fixtures or even attached or hungfrom a ceiling (in a recessed or pendant-light type format), either withor without lighting capabilities to enable the functionality describedabove. Therefore, by implementing the Concurrent Projector-Camera withinany of these types of form factors, the Concurrent Projector-Cameraenables implementations such as projections onto a table surface (or anyother surface or area) wherein multiple parties at remote locations caninteract with that projection without causing “visual echo” in theprojection provided to any of the separate locations.

In view of the above summary, it is clear that the ConcurrentProjector-Camera described herein provides robust flicker-free visualecho cancellation in separate shared or concurrent spaces in which bothimage capture and projections are being concurrently maintained over anydesired period of time. In addition to the just described benefits,other advantages of the Concurrent Projector-Camera will become apparentfrom the detailed description that follows hereinafter when taken inconjunction with the accompanying drawing figures.

DESCRIPTION OF THE DRAWINGS

The specific features, aspects, and advantages of the claimed subjectmatter will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 provides an exemplary architectural flow diagram that illustratesprogram modules and hardware for implementing various embodiments of theConcurrent Projector-Camera, as described herein.

FIG. 2 illustrates an exemplary shared workspace from two separatelocations without visual echo by using a “Concurrent Projector-Camera”at each Location, as described herein.

FIG. 3 illustrates exemplary conventional waveforms for various LED dutycycles for achieving desired brightness levels, as described herein.

FIG. 4 illustrates exemplary conventional waveforms for an RGB LEDtriplet for achieving desired perceived pixel colors during a singleimage frame, as described herein.

FIG. 5 illustrates exemplary waveforms for an RGB LED triplet that havebeen adjusted by the Concurrent Projector-Camera to create anintra-frame capture time slot for capturing an image within theprojection area, as described herein.

FIG. 6 illustrates exemplary waveforms corresponding to subfieldprojections using light control points (e.g., micromirrors or LCDshutters) with dynamic suppression of subfields, or subfield compressionwith temporal shifting of subfields, by the Concurrent Projector-Camerato open an intra-frame capture time slot for image capture, as describedherein.

FIG. 7 illustrates is a general system diagram depicting a simplifiedgeneral-purpose computing device having simplified computing and I/Ocapabilities for use in implementing various embodiments of theConcurrent Projector-Camera, as described herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description of the embodiments of the claimed subjectmatter, reference is made to the accompanying drawings, which form apart hereof, and in which is shown by way of illustration specificembodiments in which the claimed subject matter may be practiced. Itshould be understood that other embodiments may be utilized andstructural changes may be made without departing from the scope of thepresently claimed subject matter.

1.0 Introduction:

A “Concurrent Projector-Camera,” as described herein, uses an imageprojection device in combination with one or more cameras to enablevarious techniques that provide visually flicker-free projection ofrecorded or real-time images or video within a region or onto a surface,while real-time image or video capture is occurring in approximatelythat same space (which includes a sub-region of the projection area, theentire projection area or extended region encompassing the projectionarea). Note that rather than repeatedly describing the range of areas inwhich the camera or cameras are capturing the scene or projection space,the following discussion will generally simply refer to using the cameraor cameras to capture “the projection area” or “approximately the samearea” as the projection. Further, the Concurrent Projector-Cameraprovides these capabilities in a manner that eliminates video feedback(also referred to as “visual echo”) from the projection into thereal-time image or video capture. Examples of solid-state projectiondevices adaptable for use by the Concurrent Projector-Camera include,but are not limited to, LED-LCD based projection devices, DLP-basedprojection devices using LED or laser illumination in combination withmicromirror arrays, etc.

More specifically, the Concurrent Projector-Camera dynamicallysynchronizes a combination of projector solid-state lighting on-statetemporal compression in combination with on-state temporal shifting toopen an intra-frame “capture time slot” for image capture during whichno image is being projected. This capture time slot is created duringthe period in which a single image frame is being projected, andrepresents a tradeoff between image capture time and decreasedbrightness of the projected image frame. Significantly, thesecapabilities are achieved without cancelling or eliminating entireprojection frames, as is the case with various conventional techniques.

Further, in various embodiments, the total duration of the time slot canbe adjusted by first determining appropriate camera exposure times forlocal lighting conditions to determine a minimum acceptable windowduring which image capture can occur. In such embodiments, theConcurrent Projector-Camera uses conventional camera light meteringtechnologies to determine local ambient lighting conditions fordetermining proper exposure times for the camera. The capture time slotis then opened for only enough time within the time for each frame toallow image capture.

However, as discussed in further detail below, in various embodiments,the Concurrent Projector-Camera either uses light from the projector toilluminate the scene for image capture, or a dedicated light or flashtype device is used to illuminate the scene for image capture during thecapture time slot. In such cases, the capture time slot can generally beshortened, as increased local light will allow for shorter image capturetimes, as is well known to those skilled in the art.

In either case, whether determining a minimum acceptable window orproviding illumination for shortening that window, these types ofembodiments ensure that the Concurrent Projector-Camera does not openthe capture time slot for periods longer than necessary, therebylimiting the projector brightness losses resulting from opening thecapture time slot within the time for each projected image frame.

1.1 System Overview:

As noted above, the “Concurrent Projector-Camera” provides robustflicker-free visual echo cancellation in separate shared or concurrentspaces in which both image capture and projections are beingconcurrently maintained over any desired period of time. The processessummarized above are illustrated by the general system diagram ofFIG. 1. In particular, the system diagram of FIG. 1 illustrates theinterrelationships between program modules for implementing variousembodiments of the Concurrent Projector-Camera, as described herein.Furthermore, while the system diagram of FIG. 1 illustrates a high-levelview of various embodiments of the Concurrent Projector-Camera, FIG. 1is not intended to provide an exhaustive or complete illustration ofevery possible embodiment of the Concurrent Projector-Camera asdescribed throughout this document.

In addition, it should be noted that any boxes and interconnectionsbetween boxes that may be represented by broken or dashed lines in FIG.1 represent alternate embodiments of the Concurrent Projector-Cameradescribed herein, and that any or all of these alternate embodiments, asdescribed below, may be used in combination with other alternateembodiments that are described throughout this document.

Two or more Concurrent Projector-Cameras are intended to work incooperation to enable various shared workspace scenarios (e.g., oneConcurrent Projector-Camera at each remote location sharing aworkspace). Consequently, FIG. 1 illustrates several ConcurrentProjector-Cameras 100, 105 and 110 in communication via anetwork/internet 115 with an optional computing device 120 (alsoreferred to herein as a “host device”) acting as an intermediary betweenone or more of the Concurrent Projector-Cameras, and potentiallyperforming additional computations for the Concurrent Projector-Cameras.Each Concurrent Projector-Camera 100, 105 and 110 generally includesimilar elements, although there are several alternate embodiments ofthe Concurrent Projector-Cameras that are discussed in Section 2.4 suchthat there may be differences between individual ConcurrentProjector-Cameras. However, for purposes of explanation, FIG. 1 showsConcurrent Projector-Camera #1 (100) with various modules andcomponents, while illustrating Concurrent Projector-Camera #2 (105) andConcurrent Projector-Camera #N (110) as “black boxes” that are intendedto provide at least the same minimum functionality as described belowfor Concurrent Projector-Camera #1 (100).

In general, the Concurrent Projector-Camera (100, 105 or 110) includesan image projector 125 and a camera 130. While size of these devices isnot a defining feature of the Concurrent Projector-Camera (100, 105 or110), it should be noted that a relatively small projector 125 (e.g., asolid-state pico-projector), can be combined with a relatively smallcamera 130 (e.g., a webcam or any other desired camera) for integrationinto a relatively small form factor about the size of a small desktoplamp that can be placed on or clamped to a table or other surface. Suchform factors enable implementations such as projections onto a surfacewherein multiple parties at remote locations can interact with thatprojection without causing “visual echo” in the projection provided toany of the separate locations.

Regardless of the form factor in which the projector 125 and camera 130are combined, both the projector and camera are directed towards thesame general space or area. In other words, the camera 130 is configuredto capture images and/or video of the same general area where theprojector 125 projects images and/or videos. The ConcurrentProjector-Camera (100, 105 or 110) includes a projection module 135 thatprovides video of a shared workspace captured from one or more remotesites (using another Concurrent Projector-Camera) to the projector 125for projection. Note also that in various embodiments, the ConcurrentProjector-Camera (100, 105 or 110) includes an optional video insertionmodule 145 that inserts projections of one or more real or virtualobjects into the projection of the shared workspace provided by theprojection module 135.

For example, in the case that two people at remote sites are playing ashared game of chess, the Concurrent Projector-Camera (100, 105 or 110)at each site will project a virtual chessboard into the area of eachremote site, while also projecting each person's interactions with thatvirtual chess board (captured by camera 130 via a video capture module155) to the other remote site. In general a video output module 160 isused to transmit images and/or video captured by camera 130 to otherremote sites via the internet/network 115. Further, a video input module140 of each Concurrent Projector-Camera (100, 105 or 110) receives thevideo output from each other Concurrent Projector-Camera. Note that FIG.2, discussed below in Section 2.1, provides a graphical example of thistype of use of the Concurrent Projector-Camera (100, 105 or 110). Notethat this type of multi-site shared workspace uses an automaticalignment of the projector and camera so that the camera at each sitecaptures the appropriate portions of the scene for projection at eachother site.

As noted above, video capture by camera 130 occurs in a manner thatprevents possible visual echo. More specifically the ConcurrentProjector-Camera (100, 105 or 110) includes a temporal adjustment module150 that dynamically modifies projector 125 on-states (see Section 2.3)within each individual frame time to open the aforementioned intra-frame“capture time slot”. The connection from the image projector 125 to thetemporal adjustment module 150 allows the temporal adjustment module toproperly phase the capture time slot for image capture 530. Again, thecamera 130 capture images and/or videos of the area covered by projector125 during this capture time slot which itself is a subinterval of timeopened within each individual projector 125 frame time. In particular,the modified projector 125 on-states ensure that the camera 130 capturesimages at times when the area or region being imaged is not also beingsubjected to a projection from the projector 125.

Note that in various embodiments, the concurrent projector camera (100,105 or 110) also includes optional local audio capture capabilities (notshown) for capturing local audio for transmission to one or more remotesites along with the locally captured video. These audio capturecapabilities may also include various acoustic echo cancellationtechniques to enable various audio conferencing scenarios. Since suchaudio capture and acoustic echo cancellation techniques are well-knownto those skilled in the art, they will not be described in detailherein.

2.0 Operational Details of the Concurrent Projector-Camera:

The above-described program modules are employed for implementingvarious embodiments of the Concurrent Projector-Camera. As summarizedabove, the Concurrent Projector-Camera provides robust flicker-freevisual echo cancellation in separate shared or concurrent spaces inwhich both image capture and projections are being concurrentlymaintained over any desired period of time. The following sectionsprovide a detailed discussion of the operation of various embodiments ofthe Concurrent Projector-Camera, and of exemplary methods forimplementing the program modules described in Section 1 with respect toFIG. 1. In particular, the following sections provide examples andoperational details of various embodiments of the ConcurrentProjector-Camera, including: an operational overview of the ConcurrentProjector-Camera with an exemplary two-site shared workspace usagescenario; a discussion of various types of solid-state projectors asthey relate to usage with the Concurrent Projector-Camera; dynamicintra-frame control of projector on-off states for opening capture timeslots during each projected frame time; and additional embodiments andconsiderations.

2.1 Operational Overview:

As noted above, the Concurrent Projector-Camera-based processesdescribed herein provides robust flicker-free visual echo cancellationin separate shared or concurrent spaces in which both image capture andprojections are being concurrently maintained over any desired period oftime. In general, the shared work spaces enabled by the ConcurrentProjector-Camera can be maintained for two or more remote sites.

A simple example of a multi-site video communication having two sites isa shared surface showing a virtual chessboard that is concurrentlydisplayed to players at two remote locations. Alternately, a realchessboard can be included in the first of the two locations, withvirtual chess pieces being projected onto both the real board, and ontoa virtual copy of the chess board at the second location captured by thecamera of the Concurrent Projector-Camera at the first location.

For purposes of explanation, assuming the use of a virtual chessboardand pieces in both locations, each player will see a projection of thechess set and the other players interaction with that projected chessset (captured by a local camera associated with each player) without any“visual echo” resulting from either players interaction with theprojected chess set. A simple example of this type of use of theConcurrent Projector-Camera is illustrated by FIG. 2.

In particular, FIG. 2 shows two Concurrent Projector-Cameras (205 and210) at separate locations (i.e., “location 1” and “location 2”). EachConcurrent Projector-Camera (205 and 210) is projecting a virtual copyof the same chess set (220 and 225, respectively) into the sharedworkspace in each of location 1 and location 2. However, in addition tothe projected chess set (220 and 225) being projected into eachworkspace, the Concurrent Projector-Camera 210 in location 2 is alsoprojecting a real-time video of a first user's hand 235 captured by thecamera of the Concurrent Projector-Camera 205 from the first user'sactual hand 230 as it interacts with the projected chess set 220 inlocation 1. Similarly, the Concurrent Projector-Camera 205 in location 1is also projecting a real-time video of a second user's hand 245captured by the camera of the Concurrent Projector-Camera 210 from thesecond user's actual hand 240 as it interacts with the projected chessset 220 in location 2.

In the example illustration of FIG. 2, each of the ConcurrentProjector-Cameras (205 and 210) is in communication via a wired orwireless connection to an optional computing device (250 and 255,respectively), also referred to herein as a “host device,” which in turnare in communication via the internet or other network 260. In general,when used, the optional host devices perform complex image andprojection related computations to enhance the capabilities and controlof each of the Concurrent Projector-Cameras (205 and 210). As summarizedabove with respect to FIG. 1, each Concurrent Projector-Camera (205 and210) captures images of the projection area during intra-frame capturetime slots and sends those images as a streaming video of thecorresponding projection area to the other Concurrent Projector-Camerafor local projection. Since the images and/or video captured by thecamera of each of the Concurrent Projector-Cameras (205 and 210) is freefrom corruption by the ongoing projections in each of the two locations,each user simply sees a real-time projection of the chess set (220 or225) along with both their own interaction and the other user'sinteraction with that shared projected chess set.

Note that this concept can be extended beyond two separate sites, as inthe chess example described above, to many different sites that willallow many different users to interact with the same virtual workspaceor projection without causing “visual echo” in the projection providedto any of the separate sites. A simple example of this extension is avirtual round-table meeting hosting multiple persons whose images areprojected to each of the other meeting participants along with aprojection of a project plan in 2D or 3D (e.g., an interactive 3Dprojection of a city model).

By providing a Concurrent Projector-Camera at each of the separatesites, the meeting participants will be able to concurrently interactwith the projection of the project plan without causing “visual echo” inthe projection provided to any of the separate sites. Further, eachmeeting participant will be able to see the interactions of every otherparticipant with the project plan in real-time as those participantsinteract with the project plan. Further, the inclusion of a conventionalaudio system at each of the remote sites will allow the meetingparticipants to talk at the same time without interfering with theoperations of the Concurrent Projector-Cameras in any of the separatesites.

Finally, note that two cameras or a dedicated 3D camera can be used bythe Concurrent Projector-Camera to capture 3D images or video of theprojection area for real-time transmission or broadcast to other sites.However, since this type of 3D image capture does not require additionalintra-frame capture time slots to be opened, the following discussionwill generally focus on the general 2D image capture scenario. Thus, all2D image capture implementations described herein are also applicable tothe 3D case. Similarly, various embodiments of the ConcurrentProjector-Camera can be equipped with various different types of cameras(e.g., standard 2D cameras, 3D cameras, dedicated color-specificcameras, infrared or IR cameras, etc.) for particular implementations orintended uses. Consequently, the following discussion should beunderstood to apply to all such cases.

2.2 Image Projectors:

Examples of image projection devices that may be adapted for use by theConcurrent Projector-Camera include, but are not limited to, LED-LCDbased projection devices, DLP-based projection devices using LED orlaser illumination in combination with micromirror arrays or LCDshutters, etc. In other words, virtually any image projector usingeither solid-state lighting sources e.g., LED or laser) or opticallyfast light control points (e.g., micromirror arrays or LCD shutters) maybe adapted for use in implementing various embodiments of the ConcurrentProjector-Camera. Since these types of projectors are well known tothose skilled in the art, they will not be described in detail herein.However, various aspects of different types of image projectors areadapted or modified in order to implement various embodiments of theConcurrent Projector-Camera described herein. Consequently, variouspertinent features of various types of image projectors are discussedbelow.

As is well known to those skilled in the art, in the case of colorprojections, for each individual image frame, many image projectorsrapidly cycle through projections in RGB (or potentially any otherdesired color space) in a sequence that is fast enough to effectively“blend” sequential RGB projections into what the human observerperceives to be a single color. This rapid color cycling is generallyachieved either by cycling solid-state light sources, or by using arotating color wheel or the like to cycle through the colors.

Further, in the case of many solid-state projectors, the intensity orbrightness of the perceived colors is typically modulated up and down byrapidly cycling the LEDs on and off at very high frequencies while usinga consistent current level (which may be different for each of thedifferent color LEDs) to avoid color spectrum changes for the individualLEDs. In other words, when an LED is rapidly cycled on and off at afrequency beyond human visual perception, increased LED on times willsimply be perceived by the human observer as an increased brightnesslevel, while increased LED off times will simply be perceived as adecreased brightness level.

Similar brightness control are achieved in other projectors using lightcontrol points by rapidly cycling the light control point to effectivelyblank or transmit light to the human observer from whatever light sourceis being used by the projector. For example, in DLP projectors that usemicromirror arrays as a light control point where the light source(e.g., incandescent, LED, Laser, etc.) is often constantly on, eachmicromirror in the array switches on and off (i.e., moves to differentangles) multiple times during each projected image frame to project asequence of sub-fields that aggregate in the human perception to createa perceived brightness or intensity level for the pixel or pixelscorresponding to each micromirror.

More specifically, in typical DLP projectors, the image is created bymicroscopically small mirrors laid out in a matrix on a semiconductorchip that is generally referred to as a Digital Micromirror Device(DMD). Each mirror represents one or more pixels in the projected image,with the total number and layout of mirrors corresponding to an x,yresolution of the projected image. These mirrors are then rapidlyswitched or repositioned to reflect light either through the projectorlens or on to a heat sink or “light dump”. Rapidly toggling the mirrorbetween these two orientations (essentially toggling the perceived lighton and off) produces gray-scales (thus producing an apparent brightnesslevel for the observer) that are controlled by the ratio of on-time tooff-time. There are various methods by which DLP projection systems,including those used by single-chip or three-chip DLP projectors, createa color image, including sequential illumination by different colorlight sources including LEDs or lasers, and/or the use of one or morecolor wheels, etc.

For example, in the case of a projector with a single DLP micromirrorchip, colors are produced either by placing a rotating color wheelbetween a white lamp (incandescent, LED, laser, etc.) and the DLPmicromirror chip or by using individual light sources (e.g., RGB LEDs orlasers) to produce the primary colors. Color wheels are generallydivided into multiple sectors that typically include the primary colors,red, green, and blue, and in many cases secondary colors including cyan,magenta, yellow and white. The DLP micromirror chip is then synchronizedwith the rotating motion of the color wheel so that (in an RGBprojector) the green component of the image is displayed on themicromirror chip when the green section of the color wheel is in frontof the lamp. The same is true for the red, blue (and other colorsections, if used). The colors are thus displayed sequentially at asufficiently high frequency that the human observer sees a composite“full color” image. Typical DLP projectors often use color wheels thatrotate at around ten revolutions per projected image frame, though olderprojectors may run as slow as one revolution per projected image frame.

For example, a typical commercial low-cost 60 Hz (16.67 ms) LED basedprojector using MEMS micromirrors has about five internal fields (i.e.,sub-fields corresponding to each mirror switch) for each projected imageframe. In other words, at full brightness levels, a 60 Hz (16.67 ms) LEDbased projector with five internal fields per frame will switch themirrors at approximately 3.3 ms intervals (i.e., 5×3.3 ms≈16.67 ms≈60Hz).

2.3 Dynamic Intra-Frame Control of Projector On-Off States:

Note that for purposes of explanation, the following discussion willgenerally refer to the use of LED projectors, or various otherprojectors using semiconductor light sources for projection. However,any type of image projection device having a relatively high refreshrate can be used to implement various embodiments of the ConcurrentProjector-Camera described herein. Note that minimum projector refreshrates on the order of about 60 Hz (or about 120 Hz for stereo or 3Dprojections) will ensure flicker-free operation with respect to humanvisual processing of projected images using the ConcurrentProjector-Camera. However, image projectors having lower refresh ratesmay also be used if some amount of perceptible flicker is acceptable fora particular application. Clearly, image projectors having higherrefresh rates may also be used.

In view of the discussion provided in Section 2.2, it can be seen thatone feature that all types of image projectors have in common is thatintensity is generally controlled by either rapidly cycling an on-offstate of a solid-state light source (e.g., LED or laser), or by rapidlycycling light control points (e.g., micromirrors or LCD shutters) in amanner that produces an effective cycling between projector on-statesand projector off-states. Again, in view of the preceding discussion, itshould be clear that intensity or brightness of the projection decreasesin direct proportion to the total time that the projector is in anoff-state.

In general, the projector off-states (actual, mirror-based, or LCDshutter based) represent a time during which no image is being projectedon a particular surface or object (referred to herein simply as a“projection area” or simply an “area” for purposes of discussion).Consequently, if a camera captures an image of the same area covered bythe projection during a projector off-state, that image will not becorrupted by the projection. As a result, there is no possibility ofvisual echo if that captured image is itself is then transmitted andprojected onto another area from which the original projectionoriginated via capture by a second camera.

Unfortunately, with typical solid-state projection devices, theseoff-states are generally so short in duration that most cameras havedifficulty capturing enough light from the projection area to produce aquality image during a projector off-state. Therefore, to enable the useof relatively inexpensive cameras, the Concurrent Projector-Cameraprovides various techniques for dynamically adjusting projectoron-states (at the cost of reduced perceived intensity or brightness) toincrease the total intra-frame time during which the projector is in anoff-state during each individual frame. This dynamic adjustment ofprojector on-states provides an extended period during the projectiontime for each frame in which image capture can occur in the same area asthe projection without that image capture being corrupted by theprojection.

As noted above, the Concurrent Projector-Camera uses well-knowntechniques associated with photography (e.g., conventional light meters)to determine an appropriate amount of time for image capture (i.e.,camera exposure times) by whatever camera is being used by theConcurrent Projector-Camera. This amount of time is then used as aminimum window size when adjusting the on-off states of the imageprojector to open the aforementioned intra-frame capture time slot. Notethat since the determination of camera exposure times for particularlighting conditions is well known to those skilled in the art, nofurther discussion of determining minimum window sizes for capturingimages will be provided herein. Instead, the following discussion willfocus on various methods for actually opening or creating theintra-frame capture time slots.

Further, in various embodiments of the Concurrent Projector-Camera,dynamic adjustment of projector on-states is synchronized withraster-scan type projection systems such that the camera capturessub-parts of the projection area between times when the raster scanprojections are being projected onto any area being imaged by thecamera. These image sub-parts are then combined using conventionaltechniques to construct an image of the entire area.

Specific discussion and examples of various types of image projectiondevices and how they are modified for use in implementing variousembodiments of the Concurrent Projector-Camera are described below.

2.3.1 Exemplary LED Projector-Based Implementations:

As noted above, in the case of an RGB LED projector (or othersemiconductor light source based projector), the color of each pixel inthe projected image is constructed by cycling between a triplet of red,green and blue LEDs for each pixel at a rate that blends the light fromeach triplet of LEDs into a single color, as perceived by human visualprocesses. Further, also as noted above, perceived intensity orbrightness of each pixel is controlled by cycling on-off states of eachLED that blends those on-off states into a relative brightness level, asperceived by human visual processes.

For example, FIG. 3 illustrates exemplary conventional idealizedwaveforms (power vs. time) for controlling single LED on-off states tocontrol perceived brightness levels. The exemplary waveforms (300, 310,320, and 330) illustrated by FIG. 3 show LED duty cycles of 10%, 33%,50% and 95%, respectively. In particular, a particular “duty cycle” (DC)over some time period (T) indicates the length of time during whichpower sufficient to cause the LED to emit light is provided to the LED.In general, for conventional LED-based projectors, the time period T isfixed, and while the duty cycle DC is varied to achieve the desiredperceived brightness level for the LED. Note that there may be multipletime periods (T) for each image frame, depending upon the length of Tand refresh rate or frequency of the projector.

FIG. 4 illustrates a slightly more complex set of conventional idealized“power waveforms” (power vs. time) for controlling LED on-off states tocontrol perceived colors when using a set of three LEDs (e.g., in an RGBLED-based projector). For example, FIG. 4 illustrates a waveform for ared LED 400, a waveform for a green LED 410, and a blue LED 420. Asillustrated, during the time period for an image frame to be projected,the projector will cycle between the red, green, and then blue LEDs toachieve the desired perceived color (note that blue LEDs tend to haveshorter on times since they are often brighter than red or green LEDs).While FIG. 4 shows only one RGB cycle per image frame for purposes ofexplanation, there may be a number of such cycles within the time forprojecting an image frame, depending upon the projector. In any case, itcan be seen that there is little or no time during the projection of animage frame during which a camera can be used to capture an image framethat is not corrupted by a projection in one or more colors.

As illustrated by FIG. 5, the Concurrent Projector-Camera solves thisproblem by dynamically adjusting the amount of time during which eachLED is in an on-state, as well as shifting those times within the timeperiod for each image frame projection. This combination of on-statecompression and temporal shifting opens an intra-frame window of time(referred to herein as a “capture time slot”, or simply “time slot”)during which an image can be captured by the camera of the ConcurrentProjector-Camera without being corrupted by the projection of theConcurrent Projector-Camera.

For example, as illustrated by FIG. 5, the waveforms (500, 510 and 520)representing the on-state for each of the LEDs has been compressed byapproximately 20% relative to the corresponding waveforms (400, 410 and420, respectively) shown in FIG. 4. Further, as also illustrated by FIG.5, the start of the on-states for both the green LED and the blue LEDwaveforms (510 and 520, respectively) have been shifted further out intime (i.e., shifted to the right) relative to the waveforms of FIG. 4(410 and 420, respectively), with the compression of the red LEDwaveform 500 resulting in the red LED being in an off-state earlier intime. This combination of temporal compression and temporal shifting ofthe different LED on-states opens an intra-frame capture time slot 530for image capture. Note that there is no requirement to adjust all ofthe LED on-state times (i.e., any one, any two, or all three LEDwaveforms can be compressed and/or shifted). Further, there is norequirement that the amount of adjustment for each LED on-state be thesame. However, adjusting the different LEDs by different amounts maycause changes to the perceived color balance of the resultingprojection. Depending upon the projector, these types of color shiftscan be automatically corrected. Note that in the case that there aremultiple RGB cycles within the time for projecting a particular imageframe, one or more of those complete RGB cycles can be suppressedcompletely to provide the capture time slot for the camera. This conceptis similar to the suppression of subfields in projectors using lightcontrol points, described below with respect to FIG. 6.

Returning to the example of a 60 Hz LED projector having 16.67 ms frameprojection times (i.e., 1/60 Hz≈16.67 ms), a reduction or compression ofthe on-states of each LED by approximately 20% (as illustrated by FIG.5), in combination with appropriate temporal shifting of when the LEDsare turned on will open the intra-frame capture time slot of about 3.3ms in duration during which an image frame can be captured of theprojection area by an appropriately positioned and synchronized camera.Note however, that in view of the preceding discussion, the temporalcompression of the on-states of the LEDs by about 20% will result in adecrease in the perceived brightness of the projected image frame on theorder of about 20%. In other words, as noted above, intra-frame imagecapture time slots are obtained as a tradeoff against projected framebrightness or intensity, with longer capture time slots corresponding todecreased perceived brightness levels.

2.3.2 Exemplary DLP Projector-Based Implementations:

As noted above, DLP based projectors typically use solid-state lightcontrol points (e.g., micromirrors or LCD shutters) that generally cycleon and off rapidly multiple times within each projected image frame toproduce a sequence of subfields that aggregate in the human visualperception to create each perceived image frame. As noted above, thesesubfield cycles may by synchronized with color wheels, or there may beseparate light control points for each independent color illuminationsource (e.g., three separate micromirror arrays for each of a red,green, and blue light source).

Regardless of the specific configuration of the DLP-based projector, inthe case that such projectors use a sequence of subfield projections tocreate each image frame, various embodiments of the ConcurrentProjector-Camera operate by dynamically suppressing one or moresubfields within each image frame to open an intra-frame capture timeslot for the camera. In related embodiments, the ConcurrentProjector-Camera compresses the time during which each subfield is beingprojected, then temporally shifts one or more of the compressedsubfields to open the capture time slot for the camera. Note also thatboth of these embodiments (as illustrated by FIG. 6, discussed below)can be combined to create a related embodiment wherein the intra-framecapture time slot is created by compressing and shifting one or more ofthe subfields while also suppressing one or more of the subfields (notillustrated by FIG. 6, as discussed below).

For example, a typical 60 Hz LED-based DLP projector using MEMSmicromirrors has five internal fields (i.e., subfields corresponding toeach mirror switch) for each projected image frame. In other words, atfull brightness levels, a 60 Hz (16.67 ms) LED-based projector with fiveinternal subfields per frame will switch the mirrors at approximately3.3 ms intervals (i.e., 5×3.3 ms≈16.67 ms≈60 Hz). In variousembodiments, the Concurrent Projector-Camera will modify the projectoroperation in such cases to suppress (and/or compress and shift) one ormore of the subfields, thereby creating the intra-frame capture timeslot during which no projection is occurring so that the camera of theConcurrent Projector-Camera can capture image frames without corruptionby the projector. This scenario is illustrated by FIG. 6.

In particular, FIG. 6 illustrates an exemplary unmodified waveform 600showing multiple subfields (SF_(n)) during which the light control pointof the DLP projector is projecting during the time for each image frame.As noted above, in various embodiments, the Concurrent Projector-Camerasuppresses or blanks one or more of the subfields, as illustrated by themodified waveform 610 that shows suppression or blanking of subfieldsSF₃ and SF₄, relative to the unmodified waveform 600. In the timeprovided by the blanked subfields, the Concurrent Projector-Camera opensan intra-frame time slot 620 for image capture. Note that while thisexample shows five subfields for each image frame and the suppression oftwo subfields, these numbers are provided only for purposes ofillustration, and there may be more or fewer subfields in each frame,and more or fewer of those subfields can be suppressed or blanked by theConcurrent Projector-Camera to create the intra-frame time slot forimage capture.

FIG. 6 also illustrates the aforementioned embodiment wherein subfieldsare both temporally compressed and temporally shifted to open theintra-frame time slot. In particular FIG. 6 illustrates a modifiedwaveform 630 wherein each of the five subfields have been compressed byapproximately 30% in time, while being shifted either forward orbackwards in time to open an intra-frame time slot 640 betweencompressed subfields SF₃ and SF₄.

Note that the use of subfield compression in combination with subfieldtemporal shifting provides a finer granularity of control over the totaltime available for the intra-frame capture time slot than simplysuppressing or blanking one or more subfields within an image frame.Consequently, such embodiments provide a corresponding finer granularityof control over the perceived projection brightness levels. Further, itshould also be noted that in various embodiments, one or more of thesubfields can be compressed by different amounts than other of thesubfields within an image frame to open the intra-frame time slot forimage capture.

2.3.3 Exemplary Raster-Scan Type Projector-Based Implementations:

In general, both raster-scan and rolling-shutter based projectorsoperate by projecting sequential portion of an image frame. In the caseof raster scans, images are projected one pixel at a time in a sequencethat scans (or projects) pixels across rows (or columns) of theprojection area in a sequence fast enough to create a single image framein human visual perception. In the case of rolling shutter basedprojectors, complete lines or bands of the image are projected in asequence fast enough to create a single image frame in human visualperception. In other words, these types of projectors interweaveprojected pixels, lines or image bands to composite the overall imageframe at a rate that is fast enough that human vision perceives theframe to be projected all at once rather than being built up over time.With these types of projectors, various embodiments of the ConcurrentProjector-Camera are adapted to synchronize the image capturecapabilities of the camera with the raster-scan or rolling shutter-basedprojections of the shutter such that the camera captures sub-bands orregions of the projection area during intra-frame times when theprojector is projecting on other regions of the projection area. Thesecaptured sub-bands or regions are then composited in real-time to createa captured image frame of the projection area that is not corrupted bythe projection.

2.4 Additional Embodiments and Considerations:

As noted above, the Concurrent Projector-Camera includes at a minimum animage projector and a camera, as well as the capability to dynamicallymodify projector on-states to open intra-frame time slots for imagecapture within the time for each image frame. However, beyond theseminimum features, a number of additional advantageous capabilities areintegrated into various embodiments of the Concurrent Projector-Camera,as described below. Further, it should be understood that while someamount of computing capabilities can be integrated into variousembodiments of the Concurrent Projector-Camera, as illustrated by FIG.2, the Concurrent Projector-Camera can be coupled or connected to a“host device” having sufficient computational resources to performcomplex image and projection related computations in near real-time, aswell as providing a mechanism for directing and controlling variousfeatures and capabilities of the Concurrent Projector-Camera.Consequently, for purposes of explanation, it should be understood thatthe various embodiments described below may be operational either withor without a “host device,” depending upon the computational resourcesintegrated into the Concurrent Projector-Camera, or into the individualcameras or projectors of the Concurrent Projector-Camera. However,connection to a “host device” will not generally be discussed further inthe following paragraphs.

2.4.1 Super-Resolution and HDR Enhancements for the Camera:

In general, as is well known to those skilled in the art, cameras can beadapted, by using associated computational image processing, to produceimages having significantly higher resolution or higher dynamic rangethan are available by simply capturing a single image.

For example, in the case of camera “super-resolution” type operations,image resolution can be enhanced by first imparting a small known orrandom jitter (i.e., small lateral camera motions in the x,y axes).Then, by capturing multiple images of the same region having smalloffsets caused by the jitter, those images can be recombined usingvarious known super-resolution techniques to produce a composite imagehaving a higher effective resolution than any of the contributingimages.

Consequently, in various embodiments, the Concurrent Projector-Cameramakes advantageous use of such techniques by opening multipleintra-frame capture time slots within the time for each image framewhile imparting a jitter to the camera, thereby capturing multipleslightly offset images of the projection area that are uncorrupted bythe projection. Real-time computational processing of those offsetimages is then performed by the Concurrent Projector-Camera to produce asuper-resolution image of the overall projection area covered by thecamera of the Concurrent Projector-Camera. Note that the construction ofsuper-resolution images is known to those skilled in the art, and willnot be discussed in detail herein. The contribution of the ConcurrentProjector-Camera in such embodiments is the capability to dynamicallycontrol the projector on-off states to open multiple intra-frame capturetime slots during the frame projection time during which one or moreuncorrupted images can be captured.

Similarly, in the case of creating HDR images, the ConcurrentProjector-Camera again opens multiple intra-frame capture time slotswithin the time for each image frame, while capturing an image duringeach such time slot. Further, these images are either captured atdiffering illumination levels or using a series of different imagecapture times (effectively controlling the amount of light captured bythe camera) to provide a series of images that are then used toconstruct an HDR image using real-time computational processing of thoseimages. Note that the construction of HDR images is known to thoseskilled in the art, and will not be discussed in detail herein. Thecontribution of the Concurrent Projector-Camera in such embodiments isthe capability to dynamically control the projector on-off states toopen multiple intra-frame capture time slots during the frame projectiontime during which one or more uncorrupted images can be captured.

2.4.2 Scene Illumination During Capture Time Slot:

As noted above, the Concurrent Projector-Camera opens time slots duringwhich no projection is corrupting the projection area so that the cameraportion of the Concurrent Projector-Camera can capture images for use inenabling a variety of shared workspace scenarios. However, rather thanpreventing any projection during the intra-frame capture time slotsopened by the Concurrent Projector-Camera, in various embodiments, theConcurrent Projector-Camera further controls the projector to emit adesired amount of white light (or any desired lighting color of whichthe projector is capable) during each intra-frame capture time slot.These embodiments serve to better illuminate the projection area for thecamera component of the Concurrent Projector-Camera.

This concept can also be adapted to rolling-shutter type projectionsystems. In particular instead of blacking the portion of the projectionarea not receiving a projection, the intra-frame capture time slotsopened by the Concurrent Projector-Camera allows white light to shine onthose areas while the camera of the Concurrent Projector-Camera capturesan image of those areas. In other words, instead of the typical sub-bandand black-band projection of rolling-shutter type projectors, thesetypes of projectors are adapted project a white band in place of theblack band, thereby illuminating portions of the projection area notcurrently receiving a sub-band of the projection.

Note that similar scene lighting effects (visible or not) are providedfor various cameras or purposes by including dedicated lights orillumination sources of any desired color or frequency from IR throughterahertz frequency ranges in the Concurrent Projector-Camera. Theseillumination sources are then synchronized to illuminate the projectionarea for the camera or cameras during each intra-frame capture time slotopened by the Concurrent Projector-Camera.

Further, different color lights (e.g., separate red, green and bluelight sources, etc.) can be placed in offset positions within theConcurrent Projector-Camera to illuminate the scene from offset anglesusing different color lighting. Such embodiments enable a variety ofphotometric stereo based techniques. For example, as is well known tothose skilled in the art, photometric stereo is a technique in computervision for estimating the surface normals of objects in scene byobserving those objects under different lighting conditions. The use ofmultiple color lights illuminating the scene from offset positionsallows a single image to be captured with the different colors of thatimage then being processed separately to enable any desired photometricstereo based techniques. Similar effects can be achieved by using whitelights positioned at offset locations to individually illuminate thescene to capture multiple images corresponding to each separate lightsource. However, such embodiments require more intra-frame time to beopened for capturing multiple images, thereby decreasing brightnesslevels of the projection, as discussed above.

Examples of photometric stereo based techniques include, but are notlimited to, normal map generation, depth map generation, 3D rendering ofimaged objects, recovery of the shape and reflectance properties ofobjects, 3D surface texture analysis, etc. As is well known to thoseskilled in the art, these and other photometric stereo based techniqueshave a wide variety of uses that need not be described in detail herein.

2.4.4 Depth Maps and Stereo Image Capture:

In various embodiments, a depth sensor (e.g., a depth sensor such as thesensor included in Kinect™ type devices), is included in the ConcurrentProjector-Camera as an ancillary device for capturing or obtaining depthmaps of 3D objects in the projection area. These depth maps are thenused for a variety of purposes, such as, for example, to generateprojections matching the 3D object that are then projected onto the 3Dobjects in the projection area by the projector. While devices such asthe Kinect™ use structured light patterns to produce depth maps, devicesbased on other techniques may also be integrated into the ConcurrentProjector-Camera for such purposes. Examples of such devices include,but are not limited to, laser scanning techniques, stereo ormulti-camera setups, etc. In other words, any conventional process forconstructing or deriving depth information from a scene can beintegrated into various embodiments of the Concurrent Projector-Camera.

Note also that in various embodiments, the projector of the ConcurrentProjector-Camera projects structured light patterns to illuminate thescene being captured by the camera or cameras of the ConcurrentProjector-Camera during the intra-frame image capture time slot whilethe image of the scene is being captured. Again, as with devices such asthe Kinect™, illumination of a scene using structured light allows theConcurrent Projector-Camera to capture sufficient information toconstruct or derive depth maps of 3D objects in the projection area.Interestingly, by projecting a negative or opposite of the structuredlight pattern (i.e., pixels illuminated in the original pattern are darkin the negative pattern and vice versa) quickly enough during the imagecapture time slot following image capture, those patterns will blend orcancel in the human visual perception such that human observers will notsee either pattern being projected onto the scene.

Another type of camera that can be integrated into the ConcurrentProjector-Camera is known as a “time of flight” (TOF) camera. As is wellknown to those skilled in the art, a time-of-flight camera or “TOFcamera” is a camera system that creates distance data with help of thetime-of-flight (TOF) principle. The principle is similar to that ofLIDAR scanners with the difference being that the entire scene iscaptured with each laser or light pulse rather than being scanned with amoving laser. Typical TOF cameras cover ranges of a few meters up toabout several kilometers depending upon the detector material beingused. While the lateral resolution of TOF cameras is generally lowcompared to standard 2D video cameras, they are generally capable ofcapturing very large numbers of images (on the order of about 100 imagesper second or more). Such high frame rates enable a wide variety ofapplications to be provided by the Concurrent Projector-Camera,including scene motion analysis, 3D depth map construction, etc. As TOFcameras are well known to those skilled in the art, they will not bediscussed in further detail herein.

As noted above, multiple cameras can be integrated into the ConcurrentProjector-Camera for a variety of purposes. For example, by integratingmultiple cameras into the Concurrent Projector-Camera at offsetpositions, the Concurrent Projector-Camera can capture concurrent imagesof the projection area from multiple offset viewpoints during eachintra-frame image capture time slot. Therefore, given such images, depthmaps or stereo images (i.e., 3D images) of 3D objects in the projectionarea can also be constructed or captured using conventional techniques.Consequently, a Concurrent Projector-Camera at one site can capture astereo image of that site that is then projected as a stereo or 3Dprojection at another site (using conventional stereo or 3D projectiontechniques that may be integrated into the Concurrent Projector-Camera.

Another advantageous use of multiple cameras within the ConcurrentProjector-Camera is that the scene can be captured from multipleviewpoints to create one or more 3D projections that can then beprojected by 3D projectors within Concurrent Projector-Camera at othersites. Such embodiments allow uses, such as, for example, each personaround a table at a first site to view a projection from a correspondingviewpoint around a table comprising the scene being captured by theConcurrent Projector-Camera at a second site. Similarly, a person at thesecond site could move around that table to view the scene of the firstsite from the multiple positions enabled by the 3D projection derivedfrom the first site.

It should also be understood that when multiple cameras are used toconstruct various embodiments of the Concurrent Projector-Camera, thereis no requirement that the different cameras have the same capabilities.For example, the Concurrent Projector-Camera can be designed withmatching stereo cameras to capture 3D images in the visible spectrumwhile also including both an IR camera to capture or extract IR imagesor information from the scene as well as a TOF camera. In other words,any desired camera types or combinations can be combined to constructvarious embodiments of the Concurrent Projector-Camera.

2.4.5 IR Light Source Integration:

As is well known to those skilled in the art, infra-red (IR) lightsources are not visible to the unaided human eye. Consequently, an IRlight source can be included in the Concurrent Projector-Camera as anancillary device for illuminating the projection area so that an IRcamera can capture images of that area, even during projection times. Solong as the IR camera is not also sensitive to visible light from theprojector, IR images can be obtained in this manner and used for anydesired purpose.

2.4.6 Polarized Light Source Integration:

In various embodiments of the Concurrent Projector-Camera, either orboth the projector and any or all of the cameras or light sources of theConcurrent Projector-Camera are polarized. Further, in relatedembodiments, polarization angles of any of the projector, camera, orlight sources can be manually or automatically adjusted and/or matched.Note that the various techniques for adjusting polarization angles arewell known to those skilled in the art, and will not be describedherein.

2.4.7 Implementation within Small Form Factors:

Advantageously, when using small projectors (e.g., pico-projectors) incombination with relatively small cameras, the ConcurrentProjector-Camera can be implemented within a small form factor about thesize and configuration of a small desktop lamp. In fact, such a formfactor can include optional additional lighting that allows theConcurrent Projector-Camera to function as a lamp when not being usedfor other purposes such as providing scene illumination for the camera.

For example, desktop lamps come in many configurations that can eitherbe set onto a desktop surface to provide illumination of that surface,or can be clamped or attached to an edge of a desktop surface or othernearby object or wall. The Concurrent Projector-Camera can also beimplemented within other lighting-type fixtures or even attached or hungfrom a ceiling (in a recessed or pendant-light type format), either withor without optional including lighting capabilities to enable thefunctionality described above. Therefore, by implementing the ConcurrentProjector-Camera within any of these types of form factors, theConcurrent Projector-Camera enables implementations such as projectionsonto a table surface (or any other surface or area) wherein multipleparties at remote locations can interact with that projection withoutcausing “visual echo” in the projection provided to any of the separatelocations.

2.4.8 Automated Motion Control and Positional Instrumentation:

As noted above, in various embodiments, separate ConcurrentProjector-Cameras are operated from multiple sites to enable a widevariety of multi-site communications and interaction scenarios. Variousinteresting extensions to this general idea are enabled by integratingmotorized robotic-arm type controls and positional sensors into theConcurrent Projector-Camera. For example, such controls and sensorsenable movements of a Concurrent Projector-Camera at one site to beconcurrently and precisely replicated at every other site. Thus, if auser at one site moves the Concurrent Projector-Camera to pan over orzoom into a particular area during operation, that motion will bereplicated at each remote site, thereby allowing the user to effectivelyview and interact with different portions of the remote scene (orscenes) while concurrently allowing other users at the remote sites toconcurrently view and interact that scene as the ConcurrentProjector-Camera moves to provide a changing viewpoint.

Note that in various motion control embodiments, one ConcurrentProjector-Camera at one of the sites may be designated as a “master” andthe others as “slaves.” Each slave then replicates the motions of themaster. This may help avoid the possibility that two or more sites willattempt to move the Concurrent Projector-Camera at the same time, whichcould result in a disconnect between the scenes being projected at eachsite.

In addition, the positional sensors associated with ConcurrentProjector-Camera allow the cameras and/or projector to be automaticallyand precisely positioned at all concurrent sites. This allows theConcurrent Projector-Camera to capture particular camera points of view(POV) and/or to precisely position the projector to project ontoparticular surfaces and/or objects.

Further, it should be understood that various embodiments of theConcurrent Projector-Camera include position detection capabilitieswithout the motion control capabilities described above. In other words,in various embodiments, position detection techniques using conventionalsensors (i.e., potentiometers, shaft encoders, etc.) are used todetermine the precise position of the Concurrent Projector-Camera. Suchembodiments are useful for a variety of purposes, such as, for example,computing the relative distance and angle of the projection surface tothe camera and projectors of the Concurrent Projector-Camera forzooming, tilt correction, looking around 3D objects, etc.

3.0 Exemplary Operating Environments:

The Concurrent Projector-Camera described herein is operational withnumerous types of general purpose or special purpose computing systemenvironments or configurations, collectively referred to herein as a“computing device.” FIG. 7 illustrates a simplified example of ageneral-purpose computer system with which various embodiments andelements of the Concurrent Projector-Camera, as described herein, may beimplemented. It should be noted that any boxes that are represented bybroken or dashed lines in FIG. 7 represent alternate embodiments of thesimplified computing device, and that any or all of these alternateembodiments, as described below, may be used in combination with otheralternate embodiments that are described throughout this document.

For example, FIG. 7 shows a general system diagram showing a simplifiedcomputing device 700. Such computing devices can be typically be foundin devices having at least some minimum computational capability,including, but not limited to, personal computers, server computers,hand-held computing devices, laptop or mobile computers, communicationsdevices such as cell phones and PDA's, multiprocessor systems,microprocessor-based systems, set top boxes, programmable consumerelectronics, network PCs, minicomputers, mainframe computers, audio orvideo media players, gaming platforms, etc.

To allow a computing device to interact with the ConcurrentProjector-Camera, the device should have a sufficient computationalcapability and system memory to enable basic computational operations.In particular, as illustrated by FIG. 7, the computational capability isgenerally illustrated by one or more processing unit(s) 710, and mayalso include one or more GPUs 715, either or both in communication withsystem memory 720. Note that that the processing unit(s) 710 of thegeneral computing device of may be specialized microprocessors, such asa DSP, a VLIW, or other microcontroller, or can be conventional CPUshaving one or more processing cores, including specialized GPU-basedcores in a multi-core CPU.

In addition, the simplified computing device of FIG. 7 may also includeother components, such as, for example, a communications interface 730.The simplified computing device of FIG. 7 may also include one or moreconventional computer input devices 740 (e.g., pointing devices,keyboards, audio input devices, video input devices, haptic inputdevices, devices for receiving wired or wireless data transmissions,etc.). The simplified computing device of FIG. 7 may also include otheroptional components, such as, for example, one or more conventionalcomputer output devices 750 (e.g., display device(s) 755, audio outputdevices, video output devices, devices for transmitting wired orwireless data transmissions, etc.). Note that typical communicationsinterfaces 730, input devices 740, output devices 750, and storagedevices 760 for general-purpose computers are well known to thoseskilled in the art, and will not be described in detail herein.

The simplified computing device of FIG. 7 may also include a variety ofcomputer readable media. Computer readable media can be any availablemedia that can be accessed by computer 700 via storage devices 760 andincludes both volatile and nonvolatile media that is either removable770 or non-removable 780, for storage of information such ascomputer-readable or computer-executable instructions, data structures,program modules, or other data. By way of example, and not limitation,computer readable media may comprise computer storage media andcommunication media. Computer storage media includes, but is not limitedto, computer or machine readable media or storage devices such as DVD's,CD's, floppy disks, tape drives, hard drives, optical drives, solidstate memory devices, RAM, ROM, EEPROM, flash memory or other memorytechnology, magnetic cassettes, magnetic tapes, magnetic disk storage,or other magnetic storage devices, or any other device which can be usedto store the desired information and which can be accessed by one ormore computing devices.

Storage of information such as computer-readable or computer-executableinstructions, data structures, program modules, etc., can also beaccomplished by using any of a variety of the aforementionedcommunication media to encode one or more modulated data signals orcarrier waves, or other transport mechanisms or communicationsprotocols, and includes any wired or wireless information deliverymechanism. Note that the terms “modulated data signal” or “carrier wave”generally refer to a signal that has one or more of its characteristicsset or changed in such a manner as to encode information in the signal.For example, communication media includes wired media such as a wirednetwork or direct-wired connection carrying one or more modulated datasignals, and wireless media such as acoustic, RF, infrared, laser, andother wireless media for transmitting and/or receiving one or moremodulated data signals or carrier waves. Combinations of the any of theabove should also be included within the scope of communication media.

Further, software, programs, and/or computer program products embodyingthe some or all of the various embodiments of the ConcurrentProjector-Camera described herein, or portions thereof, may be stored,received, transmitted, or read from any desired combination of computeror machine readable media or storage devices and communication media inthe form of computer executable instructions or other data structures.

Finally, the Concurrent Projector-Camera described herein may be furtherdescribed in the general context of computer-executable instructions,such as program modules, being executed by a computing device.Generally, program modules include routines, programs, objects,components, data structures, etc., that perform particular tasks orimplement particular abstract data types. The embodiments describedherein may also be practiced in distributed computing environments wheretasks are performed by one or more remote processing devices, or withina “cloud” of one or more devices (i.e., a “cloud computing”environment), that are linked through one or more communicationsnetworks. In a distributed computing environment, program modules may belocated in both local and remote computer storage media including mediastorage devices. Still further, the aforementioned instructions may beimplemented, in part or in whole, as hardware logic circuits, which mayor may not include a processor.

The foregoing description of the Concurrent Projector-Camera has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the claimed subject matter to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. Further, it should be noted that any orall of the aforementioned alternate embodiments may be used in anycombination desired to form additional hybrid embodiments of theConcurrent Projector-Camera. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

1. A concurrent projector-camera device for projecting a video onto anarea while concurrently capturing a sequence of images of approximatelythe same area without being corrupted by the projection, comprising: afirst image projection device for projecting a first image sequence ontoa first area; one or more cameras positioned to capture a second imagesequence of approximately the same first area covered by the projectionof the first image sequence; and a first temporal adjustment module fordynamically modifying on-states of the first image projection devicewithin each individual frame time of the projection of the first imagesequence to open an intra-frame “capture time slot” during which eachimage frame of the second image sequence is captured without beingcorrupted by the projection of a corresponding frame of the first imagesequence.
 2. The concurrent projector-camera device of claim 1 furthercomprising a first video output module for transmitting the second imagesequence to a second concurrent projector-camera device, and wherein thesecond image sequence is then projected onto a second area by the secondconcurrent projector-camera device for creating a shared projectedworkspace between the first and second areas.
 3. The concurrentprojector-camera device of claim 2 wherein the second concurrentprojector-camera device captures the first video sequence of the secondarea during intra-frame capture time slots opened by a second temporaladjustment module of the second concurrent projector-camera, and whereinthe first video sequence is then transmitted to the first imageprojection device for projection onto the first area for creating theshared projected workspace between the first and second areas.
 4. Theconcurrent projector-camera device of claim 1 wherein the concurrentprojector-camera is implemented within a desktop lamp type assembly. 5.The concurrent projector-camera device of claim 1 further comprising adevice for constructing a depth map of 3D objects in the first area. 6.The concurrent projector-camera device of claim 1 further comprising oneor more light sources synchronized to the capture time slot forilluminating the first area while each frame of the second imagesequence is being captured.
 7. The concurrent projector-camera device ofclaim 6 further comprising a device for adjusting a polarity of the oneor more of the light sources.
 8. The concurrent projector-camera deviceof claim 1 further comprising a device for causing the first imageprojection device to project a white light during each capture timeslot.
 9. The concurrent projector-camera device of claim 1 furthercomprising a device for causing the first image projection device toproject at least one structured light pattern onto the first area duringeach capture time slot.
 10. The concurrent projector-camera device ofclaim 1 wherein the first image projection device is an LED-basedprojector having separate red, green and blue LEDs.
 11. The concurrentprojector-camera device of claim 10 wherein dynamically modifyingon-states of the first image projection device further comprisesautomatically modifying power waveforms of each separate LED bycompressing LED on-times and optionally temporally shifting thecompressed LED on-times to open each intra-frame capture time slot. 12.The concurrent projector-camera device of claim 1 wherein the firstimage projection device uses light control points to project a pluralityof subfields for each projected frame of the first image sequence. 13.The concurrent projector-camera device of claim 12 wherein dynamicallymodifying on-states of the first image projection device furthercomprises automatically suppressing one or more subfields of eachprojected frame of the first image sequence to open each intra-framecapture time slot.
 14. The concurrent projector-camera device of claim12 wherein dynamically modifying on-states of the first image projectiondevice comprises automatically compressing on-times of one or more ofthe subfields and temporally shifting the compressed subfields to openeach intra-frame capture time slot.
 15. The concurrent projector-cameradevice of claim 1 further including a plurality of light sourcespositioned in relative offset positions, said light sources beingsynchronized with the one or more cameras to enable a host devicecoupled to the concurrent projector-camera device to perform photometricstereo-based computations relating to the second image sequence.
 16. Adevice for capturing a video of a scene on which an image sequence isconcurrently being projected, comprising: one or more projectors; one ormore cameras; a temporal adjustment module that dynamically creates anintra-frame “capture time slot” during each frame of a projection by theone or more projectors of a first image sequence onto a first area;wherein the one or more cameras captures each frame of a second imagesequence of the first area during a corresponding one of the intra-framecapture time slots; and wherein each intra-frame capture time slotrepresents a period of time during which each corresponding image frameof the second image sequence is captured without being corrupted by theprojection of any frame of the first image sequence.
 17. The device ofclaim 16 further comprising an automated motorized control forautomatically positioning the one or more cameras and the one or moreprojectors relative to the first area.
 18. The device of claim 16wherein one or more of the projectors automatically project at least onestructured light pattern onto the first area during each intra-framecapture time slot for use in deriving depth information for objectswithin the first area from the second image sequence of the first area.19. A device for eliminating visual echo when capturing a video of anarea on which an image sequence is being projected, comprising: one ormore projectors that project a first image sequence onto a first area;one or more cameras that capture each frame of a second image sequenceof the first area during a corresponding intra-frame “capture timeslot”; a temporal adjustment module that dynamically creates eachintra-frame capture time slot during each frame of the projection of thefirst image sequence; and wherein each intra-frame capture time slotrepresents a period of time during which each corresponding image frameof the second image sequence is captured without being corrupted by theprojection of any frame of the first image sequence.
 20. The device ofclaim 19 wherein: one or more of the projectors is an LED-basedprojector having separate red, green and blue LEDs; and whereindynamically creating each intra-frame capture time slot furthercomprises automatically modifying power waveforms of one or more of theseparate LEDs by individually compressing LED on-times and temporallyshifting the compressed LED on-times to open each intra-frame capturetime slot.